Rotary potentiometer



' Nov. 8, 1960 F. H. KARG 2,959,729

ROTARY POTENTIOMETER Filed Nov. 6, 1959 a g J L\\\h\\ fu INVENTOR.

Unite ROTARY POTENTIGMETER Filed Nov. 6, 1959, Ser. No. 851,379

7 Claims. (Cl. 323-79) This invention has to do generally with rotarypotentiometers, comprising a resistance element that is curved,typically in a circular arc, and is engaged by an angularly movablebrush, typically rotatable about the axis of ourvature of the resistanceelement.

The invention relates more particularly to rotary potentiometers thatare operable through an angle of substantially 360 or more.

The invention is particularly useful in connection with potentiometerswherein the brush is continuously rotatable, producing an output that isa periodic function of the brush angle, with a period of 360".

A primary difficulty in constructing such potentiometers in the past hasbeen the tendency of the brush to make contact with one end of theresistive element before it breaks contact with the other end. The brushthus tends to contact both ends of the element simultaneously, shortcircuiting the input terminals to the element. Alternatively, if theends of the element are spaced apart circumferentially by a sufficientamount to prevent such short circuiting action, the brush tends to bemomentarily out of contact with the element, interrupting the desiredsignal output.

The present invention avoids those and other difliculties in aparticularly effective and convenient manner. That is typicallyaccomplished by providing two distinct resistive elements or windingsegments, which are conneoted in series. The potentiometer is typicallyprovided with two input terminals which are connected to the respectivewinding segments adjacent opposite ends thereof, the other end portionsof the winding segments being connected together. Those connections tothe winding segments may be angularly adjustable, if desired. Separatebrushes are provided for the respective winding segments. Each windingsegment is made less than 360 in extent, the sum of the effectiveworking portions of the winding segments being substantially equal to360. The winding segments are preferably arranged coaxially, but arespaced from each other transversely of their length, such spacing beingtypically either axial or radial in direction. Thus each brush can swingbeyond the angular limits of its winding segment without contacting theother winding segment.

In accordance with the invention, the two brushes are connected inparallel to the effective output terminal of the potentiometer, meansbeing provided in such connec-v tion to prevent current flow from one ofthe brushes to the other.

In preferred form of the invention, the two winding segments are carriedon respective supports which are mounted coaxially in a mannerpermitting mutual angular adjustment. The two brushes are typicallymounted on a common shaft, on which they may also be angularlyadjustable. One or both of the winding supports may comprise portionsor" a housing structure that encloses the windings and brushes andprovides bearing supports for the brush shaft.

A full understanding of the invention, and of its furice ther objectsand advantages, will be had from the follow ing description of certainillustrative manners in which it may be carried out. The particulars ofthat description, and of the drawings which form a part of it, areintended only for illustration, and not as a limitation upon the scopeof the invention, which is defined in the appended claims.

In the drawings:

Fig. l is a schematic drawing representing an illustrative embodiment ofthe invention;

Fig. 2 is an axial section representing an illustrative manner ofconstructing a potentiometer in accordance with the invention; and

Fig. 3 is a transverse section, taken on the line 3-3 of Fig. 2.

Fig. 1 represents the invention illustratively in the form of aschematic diagram, wherein the characteristically cylindrical form ofthe device has been developed onto a plane for clarity of illustration.Thus, the vertical lines denoted 0 and 360 represent a common axialplane of the actual device. The potentiometer winding comprises the twowinding segments 10 and 20. Opposite end points 11 and 21 of the twowinding segments are connected to the respective terminals 12 and 22 bythe lines 13 and 23. Those terminals will be referred to for convenienceas power or input terminals, since they are ordinarily, although notnecessarily, connected to a suitable source of electrical power toproduce a voltage drop in the potentiometer winding. Adjacent end points15 and 25 of the two winding segments are connected together by the line14, so that current can flow between power terminals 12 and 22 throughthe two winding segments in series. The angular relationship between endpoints 15 and 25 is determined, in a manner to be described, withrelation to the respective brush actions; but those end points may bevaried together as may be desired. One winding segment may, for example,extend only a few degrees, the length of the other being correspondinglyincreased so that their sum is substantially 360.

The described opposite end points 11 and 21 and the adjacent end points15 and 25 of the winding segments are not all necessarily at the extremephysical termination points of the actual winding structures. However,it is convenient to refer to those points as end points of the windingsegments, since, as connection points of the described lines 13, 14 and23, they define the effective ends of the actual working portions of thewinding segments, as will appear more fully below. In the presentillustrative instance, winding 10 extends to the right in Fig. 1 beyondend point 15, as shown at 41; and extends to the left beyond end point11, as shown at 42. The portion 42 appears at the right edge of thedeveloped diagram, but its right hand extremity is physically connectedto left end point 11 of the winding proper.

The brush assembly 30, as represented in Fig. 1, comprises the twobrushes 17 and 27, which are adapted to slidingly engage the respectivewinding segments 10 and 20. Brushes 17 and 27 are mechanically linkedtogether with respect to their movement, as indicated schematically bythe dashed line 24. As shown, the brushes are electrically connected inparallel to the terminal 32 via the respective lines 18 and 2%. Terminal32 will be referred to as an output terminal, but without implying anylimitation upon the function or manner of connection of thepotentiometer in any actual electrical system.

A unidirectional conduction device is provided in at least one of thelines 18 and 28. Such devices may be of any suitable type, such asvacuum tube or semiconductor diodes, for example. In the presentembodiment, a single unidirectional device is represented schematicallyat 19 in line 18, oriented to permit current liow only in the directionfrom brush 17 toward terminal 32.

Suitable guide surfaces for the brushes are typically provided in thoseportions of the brush movernent beyond the physical boundaries of therespective winding segments. Such surfaces, represented as the guidebars 34 and 35, may be formed of dielectric material; or may compriseportions of initially continuous windings which have been severed toinsulate them from other electrical components of the assembly.

In operation of the potentiometer, power terminals 12 and 22 aretypically connected via the lines 36 and 37 to suitable sources of lowand high potential, respectively, such, for example, as the groundednegative terminal and the positive terminal of a battery, as representedschematically at 33. Output terminal 32 is typically connected to anegative reference potential or ground via a load resistance, indicatedat 44, which is high compared to the total resistance of thepotentiometer winding. Resistance 44 may, for example, comprise the gridleak of a vacuum tube input circuit.

In discussing the brush action it will be convenient to distinguish thewinding segments and their respective brushes by the terms upper andlower, referring to their position as shown in Fig. 1, but not implyingany necessary orientation of an actual potentiometer. With brushassembly 3% in the typical position shown in Fig. 1, lower brush 17engages winding segment 10, while upper brush 27 is isolated fromsegment 20, riding on insulated bar 35. The potential of output terminal32 is therefore lifted above ground to the potential of that point oflower winding segment at which it is engaged by brush 17. That potentialrises gradually as the brush moves to the right toward end point 15.

The apparatus is preferably so dimensioned and adjusted that rightwardbrush movement causes upper brush 27 to first engage winding 20 at itsend point 25 just as lower brush 17 reaches end point 15. Suchengagement causes no appreciable change in the potential at outputterminal 32, since the points and 25 are at a common potential, due toconnection 14. Further brush movement to the right as seen in Fig. 1causes the output potential at terminal 32 to increase smoothly inaccordance with the potential tapped by upper brush 27. Lower brush 17typically continues for a short time to engage its winding 10, due tothe finite width of the brush; and may move for an appreciable angulardistance over the portion 41 of the winding to the right of 15, if suchportion is present. But neither of those actions significantly affectsthe output signal at 32, since the blocking action of diode 19 preventsbrush 17 from lowering the output potential below that set by brush 27.The exact length of winding portion 41 is therefore immaterial, so faras operation is concerned, and may have any convenient value. Windingportion 41 may be omitted altogether, if desired, though its presencegenerally facilitates smooth and continuous action of the potentiometer,as well as its construction and adjustment. After lower brush reachesinsulated bar 34, the output continues to be controlled by upper brush27 and winding segment 20.

As the brush movement approaches the lines 0 and 360 of Fig. 1, lowerbrush 17 again engages winding segment 10, this time at the portion 42which extends leftward beyond end point 11. However, the outputpotential continues to be controlled by upper brush 27, since therelatively low potential of portion 42, corresponding to groundpotential in the present instance, cannot be immediately communicated tooutput terminal 32, due to the blocking action of diode 19. The lengthof portion 42 may have any convenient value, including zero.

When upper brush 27 leaves winding 20, that controlling circuit isopened, and the potential of output terminal 32 is free to drop, due tocurrent through resistance 44 and reverse current through diode 19, tothe value set by lower brush 17. The apparatus is preferably soarranged, with due regard for the finite brush widths, that brush 17 hasthen just reached end point 11 of winding 10. Further brush movementthen causes smooth increase of output potential from the minimum levelof input terminal 12. It is therefore evident that right hand brushmovement produces a continuous output at terminal 32 that correctlyrepresents the brush position at all times.

Movement of brush assembly 30 to the left as seen in Fig. 1 also causessmooth changes of output potential without any possibility of shortingthe power terminals and without gaps or irregularities in the controlaction. As the brushes move leftward from the position illustrated,upper brush 27 engages end point 21 of winding 20 taking over effectivecontrol of the output potential regardless of the fact that lower brush17 may continue to engage winding portion 42, since the lower voltage ofthat portion is blocked by diode 19. And upper brush 27 gives up controlof the output potential only after breaking contact with winding 20 atend point 25, regardless of the fact that lower brush 17 may previouslyhave reached winding portion 41.

The extensions 41 and 42 may be shorted, as with solder, for example, sothat their effective voltage is independent of current drawn by thebrush.

If it should be desired for any reason to reverse the connection of thepotentiometer winding in the external circuit, so that power terminal 12is positive with respect to terminal 22, it is only necessary to reversethe polarity of unidirectional device 19, so that it permits currentflow from output terminal 32 toward brush 17. Then, as in thearrangement illustrated, upper brush 27 controls the output potentialwhenever it is engaging its winding segment 20. That arrangement, withboth the supply voltage and diode 19 reversed from their illustrateddirections, is useful, for example, when the output terminal 32 is to beconnected to a circuit which tends to raise the potential of theterminal, rather than to lower it, as was assumed in the precedingdescription of Fig. 1. Thus, for example, when the output load,represented at 44, is returned to a relatively negative referencepotential, the arrangement of Fig. 1 is appropriate; when that referencepotential is relatively positive, the inverted arrangement isappropriate. To facilitate reversal of the polarity of unidirectionaldevice 19, a reversing switch, which may be of conventional type, may beprovided, as indicated schematically at 46.

For many purposes it is unnecessary to provide extensions of one windingin both directions beyond the end points of its working portion, asillustratively shown at 41 and 42 in Fig. 1. For example, both of thoseportions can be omitted, and accurate construction and adjustment can berelied upon to give smooth and accurate transition from one brush to theother. It is usually helpful, however, to provide a winding extension atleast at 41, which controls the brush transition that occurs at apotential intermediate the supply potentials at power terminals 12 and22. And it is ordinarily preferred to provide extensions of one windingsegment in both directions.

Figs. 2 and 3 represent an illustrative structure for carrying out theinvention. Two mounting members 50 and 60 carry the respective windingsegments 52 and 62, which typically correspond to segments 10 and 20 ofFig. 1. Those winding segments may comprise resistive elements of anysuitable type, including, for example, carbon resistors as well aswire-wound assemblies. When wire-wound resistance elements are employed,they may typically be toroidally wound on annular forms of conventionaltype, or may be wound on initially straight forms which are then bent tocircular shape. Each of the winding segments may be made from a completewinding, substantially 360 in angular extent, which is then severed atone or more selected angular positions to electrically isolate a portioncorresponding to the insulative guide rail 34 or 35 of Fig. 1. Thewinding segments are typically mounted in their supports 50 and 60 bymeans of insulative mounting rings 53 and.63, respectively.

As shown, support 59 is of cup form, with a coaxial bore at 54 adaptedto receive a bearing 55. Support 60 is of sleeve form with a flange 64at one end adapted to coaxially engage the circular edge 56 of support50, thus providing an angularly adjustable connection between the twosupports. That adjustment can be locked, as by the set screws 66.

A circular end plate or cap '70 is mounted on support 60 at its endopposite to flange 64, as by the set screws '72. Cap '79 and the twosupport members form a closed housing enclosing the two resistanceelements 52 and 53 and the brush structure to be described. A bearingseat for a second ball bearing 74 is typically provided coaxially on theinner face of cap 7 0.

A potentiometer shaft 80 is rotatably mounted in the bearings 55 and 74,with one end accessible outside the housing. Two brushes 82 and 84,which may be of conventional type, are mounted on shaft 80, as by thespring arms 83 and the collars 85 of insulative material, in position toengage edges of the respective winding segments 52 and 62. At least oneof the brushes may be angularly adjustable with respect to shaft 80; asby release of the set screw 86, thereby facilitating the production ofany desired mutual angular relation of the brushes, which correspond tobrushes 1'7 and 27 of Fig. 1. However, that adjustment is unnecessary inthe present embodiment, since relative rotation of the two housingmembers 59 and 60 provides an equivalent fine adjustment moreconveniently.

Three insulated terminal structures are provided for each windingsegment, and are typically mounted in bores in the side walls of supportmembers 50 and 60. As illustratively shown, one terminal structure 90 ofeach set carries a light metal spring 87 of V-form. Spring 87 slidinglyengages a groove in the metal slip ring 88, by which each brush iscarried on the collar 85. Two terminal structure of each set, indicatedat 91 and 92 in Fig. 3, facilitate the electrical connections, alreadydescribed, to the end points of each resistance element. Thoseconnections may be made permanently, as with solder.

If it should be desired to make those connections adjustable, anyavailable mechanism for that purpose may be utilized. Such mechanism isrepresented illustratively as a screw clamp fitting, indicatedschematically at 96, which is representative of a wide variety ofstructures by which contact may be made at a variable point of aresistive element.

The terminal structures that are connected to the winding end pointscorresponding to and of Fig. 1, may be connected together directly,either internally or externally of the housing; and if that connectionis internal, those terminal structure need not extend through thehousing wall. The two terminal structures carrying contact springs 87 tothe brushes are similarly connected together via the unidirectionaldevice already described, which may itself be either internal orexternal of the housing as preferred. That device, corresponding to 19of Fig. 1, is represented schematically at 94 in Fig. 2, connectedexternally between the terminal structures 90. The appropriate one ofthose two terminal structures may then be utilized as the outputterminal of the potentiometer, corresponding to terminal 32 of Fig. 1.The two terminal structures that are connected to the winding end pointscorresponding to 11 and 21 of Fig. 2 may be utilized as power or inputterminals of the potentiometer.

It will be understood that many changes may be made in the particularsof the illustrative structures that have been described withoutdeparting from the proper scope of the invention. For example, manydifferent techniques are known for shaping potentiometer windings,including the use of forms of varying section and of non-circular shape.

I claim:

1. Rotary potentiometer means, comprising in combination, twosubstantially circularly curved resistive elements, structure mountingthe elements in coaxial relation with respect to an axis, two inputterminal mean connected to end connection points adjacent opposite endsof the respective elements, means electrically interconecting theelements at respective connection points thereof that are angularlyspaced from said end connection points by respective angles whose sum issubstantially 360 degrees, two brush means angularly movable over therespective elements, means for rotating both brush means about the axisin fixed mutual angular relation, output terminal means, and circuitmeans connecting the output terminal means to both said brush means,said circuit means including means acting to prevent current flow fromone brush means to the other.

2. Rotary potentiometer means as defined in claim 1, and wherein thelast said means comprises a unidirectional device connected in serieswith one of the brush means.

3. Rotary potentiometer means as defined in claim 1, and wherein one ofthe resistive elements extends angularly beyond at least one of the saidconnection points thereof.

4. Rotary potentiometer means as defined in claim 1, and wherein one ofthe resistive elements extends angularly beyond at least one of said endpoints thereof, and wherein the last said means of claim 1 comprises auni directional device connected in series with the brush means of saidone resistive element.

5. Rotary potentiometer means comprising in combination, two rotarypotentiometer units each comprising a support, an electrical resistiveelement mounted on the support and brush means angularly movable overthe resistive element, means for mounting the supports coaxially indefinite angular relation, means for driving the two brush means indefinite mutual angular relation, two input terminal means connected toopposite end points of the respective resistive elements, meanselectrically interconnecting the resistive elements at respectiveconnection points thereof that are angularly spaced from said end pointsby respective angles whose sum i substantially 360 degrees, and outputterminal means connected in parallel to the brush means of bothpotentiometer units.

6. Rotary potentiometer means as defined in claim 5, and including aunidirectional device connected between the output terminal means andthe brush means of at least one potentiometer unit.

7. Rotary potentiometer means as defined in claim 5, and including meansfor adjustably varying the mutual angular relation of the supports.

References Cited in the file of this patent UNITED STATES PATENTS1,604,196 Potter Oct. 26, 1926 1,695,875 Aiken Dec. 18, 1928 2,012,392.Israel Aug. 27, 1935 2,769,131 Immel Oct. 30, 1956 2,850,604 RowleySept. 2, 1958 FOREIGN PATENTS 679,393 Germany Aug. 4, 1939

